Aluminum alloys



Patented Aug. 29, 1933 PATENT OFFICE ALUMINUM ALLOYS Howard J. Rowe,Lakewood, Ohio, assignor to Aluminum Company of America, Pittsburgh,Pa., a corporation of Pennsylvania No Drawing.

Application September 21, 1932 Serial No. 634,172

1 Claim.

The invention relates to aluminum base alloys, and more specifically tosuch alloys containing substantial amounts of silicon and lesser amountsof copper and magnesium.

The invention is particularly concerned with aluminum base alloyscontaining from about 3 per cent to about 8 per cent of silicon, fromabout 0.5 per cent to about 3.0 per cent of copper, and from about 0.2per cent to about 1.5 per cent of magnesium.

It is the principal object of this invention to effect an improvement inalloys in the above range by the addition of manganese and nickel,either separately or in combination. The manganese may be added inamounts between about 0.3 per cent and 2.0 per cent. The nickel may beadded in amounts between about 0.3 per cent and 3.0 per cent. Ifmanganese and nickel are added in combination, the amount of each shouldnot exceed the amount disclosed immediately hereinabove for eachelement, and the sum total of both elements should be between 0.3 percent and 4.0-

per cent.

The group of aluminum base alloys containing silicon, copper, andmagnesium in amounts as indicated hereinabove forms an extremely usefulseries of alloys. In the molten condition at about ordinary pouringtemperatures they exhibit .a high degree of fluidity. and such othercharacteristics as go to make up a good casting alloy. They have anexceptionally high elongation and their other physical properties, suchas tensile strength and hardness are satisfactorily commensurate withthe improved elongation. They exhibit a relatively high resistance tocorrosion. I

These alloys are susceptible to such varied commercial adaptations'thatthey have come to be used in many forms, some of them involving serviceat fairly elevated temperature. They have been formed, forinstance,.into cylinder heads, or other parts for internal combustionengines where temperatures up to, and perhaps exceeding 600 Fahrenheitare encountered.

I have found that the strength of the aluminum-silicon-copper-magnesiumalloys as disclosed hereinabove, while heretofore. regarded as adequatefor ordinary needs, may be improved particularly in the highertemperature ranges, by the addition of manganese and nickel or by eitheralone. From a consideration of alloying ingredients or room temperatureproperties it is extremely difilcult if not impossible topredict thebehavior of an aluminum base alloy at elevated temperatures, forinstance at 400 Fahrenheit or 600 Fahrenheit. Experience has shown thatmany alloys of excellent casting characteristics and good roomtemperature properties fall off very rapidly in strength as thetemperature is raised. It is only very rarely that an alloy is dis-Covered which combines favorable properties under all temperatureconditions and is at the same time characterized by excellent castingproperties.

An alloy was made up to contain 5.0 per cent of silicon, 1.3 per cent ofcopper and 0.5 per cent of magnesium, the balance being commercialaluminum. For convenience this alloy is termed alloy A. Test specimenswere cast in sand from this alloy and were then given a homogenizingtreatment of 2 hours at 550 Fahrenheit. They were then heated to 600Fahrenheit and tested at that temperature. The average of a number oftensile tests showed a tensile'strength of 8,490 pounds per square inch.Other test specimens identical in all respects except that theycontained 0.6 per cent manganese were tested under similar thermalconditions and hadv an average tensile strength of 8,770 pounds persquare inch. Another set of test specimens without manganese but with0.8 per cent of nickel in addition to the silicon, copper and magnesiumas in alloy A, had an average tensile strength of 8,950 pounds persquare inch after an identical thermal treatment. A set of specimens ofidentical silicon, copper and magnesium as alloy A, but containing 0.6per cent manganese and 0.8 per cent nickel after the disclosed thermaltreatment had a tensile strength of 10,510 pounds per square inch.

Another set of sand cast specimens of aluminum base alloy were made upto contain silicon, copper, and magnesium as in alloy A. They were givena thermal treatment of 8 hours at 440 Fahrenheit, 2 hours at 550Fahrenheit, and 10 days at 600 Fahrenheit, being tested at the lattertemperature. They had an average tensile strength of 6,282 pounds persquare inch. -Another set of similar composition and similarly treatedthermally but containing 0.6 per cent manganese had a tensile strengthof 8,620 pounds per square inch. By a comparison with the last paragraphit can be observed that whereas alloy A, without manganese, lost 2,280pounds per square inch after an extended period at elevatedtemperatures, the same alloy with 0.6 per-cent added manganese lost only150 pounds per square inch.

An alloy similar in all respects to alloy A except that it contained 0.6per cent manganese and 0.8 per cent nickel was given a thermal treatmentof 2 hours at 550 Fahrenheit followed by varying times at 600Fahrenheit. After 3 days at 600 Fahrenheit the average strength was8,880 pounds per square inch, after 10 days at 600 Fahrenheit it was8,970 pounds per square inch, and after 30 days at this temperature thestrength was 9,240 pounds per square inch. It is not to be expected thatby lengthening the time of treatment the strength will keep ascending asthe tendency seems to hold in this last example. As a matter of fact theordinary efiect of increasing the time at temperature is to weaken thespecimen and'alloy A after 30 days at 600 Fahrenheit had a tensilestrength of only 5,957 pounds per square inch as compared with 9,240pounds per square inch for alloy A with added nickel and manganese. Thedifferences between 8,880, 8,970,

and 9,240 pounds per square inch for 3, 10 and 30 days respectively at600 Fahrenheit are all between specimens identical in every respect, andthe results are given merely to illustrate that by the addition ofnickel and manganese an alumi-- num base alloy containing silicon,copper and magnesium within the disclosed range becomes much moreresistant both to the deteriorating efiect of elevated temperatures andthe additional weakening efiect of extended time at these temperatures.By actual test the tensile strength of alloy A decreased from 9,577pounds per square inch to 5,957 pounds per square inch on a seriesextending from 30 minutes at 600 Fahrenheit to 30 days at 600 Fahrenheitwhile alloy A, with manganese and nickel in excess of 0.6 per cent ofeach, decreased from 10,330 to 9,240 pounds per square inch. In otherwords, alloy A lost about 3'? per cent of its strengthbetween 30 minutesand 30 days at 600 Fahrenheit, while alloy A with manganese and nickellost only 10 per cent of its strength over the same period.

These tests and others within my experience indicate a double advantagein favor of the addition of manganese and nickel to aluminum base alloyscontaining silicon, copper and magnesium. The addition of manganese andnickel increases the strength of the alloy at room temperature andelevated temperatures. In addition the presence of manganese and nickelin the alloy lessens the tendency of the alloy to deteriorate onextended exposure to elevated temperatures. In other words while theadvantage of the addition of manganese and nickel becomes immediatelyapparent, this advantage becomes. more obvious with increasing time attemperature.

purity. The beneficial effects of the invention are observable over arange of from about 3 per cent to. about 8 per cent of silicon, fromabout 0.5 per cent to about 3.0 per cent of copper, from about 0.2percent to 1.5 per cent of magnesium, from about 0.3 to 2.0 per cent ofmanganese and from about 0.3to 3.0 per cent of nickel. The alloyingconstituents silicon, copper, and magnesium may be varied to suit thepurposes of the user, such variations affecting the casting propertiesand other physical characteristics such as susceptibility to improvementby thermal treatments. The general eifect of increasing the nickel andmanganese content is to increase the strength and hardness of the alloyand decrease its ductility.

The alloys herein disclosed are susceptible to variation of propertiesand internal structure by thermal treatments known to the art. Theeffect of the so-called solution treatment, namely a soaking treatmentat 980 Fahrenheit or thereabouts followed by rapid cooling is to improvethe room temperature properties, but the effect induced by a treatmentof this type is counteracted by extended exposure to temperaturesaboveabout 400 Fahrenheit.

The alloying constituents may be added to the molten aluminum in thecustomary manner, the silicon, copper, magnesium, and nickel by means ofrich alloys" and the magnesium either in this manner or in'the purestate. The technique may be varied to suit foundry practice.

In the appended claims the term alloy includes the alloy in anycondition whether cast in sand or other type of mold, whetherheat-treated or unheat-treated and whether modified by ingredientsfamiliar in the use of alloys containing silicon, or unmodified.

